Milling hine Speeds

[david newman 9Participant @davidnewman9]

I have had my milling machine for years a Mikron the man I bought it from had converted it from flat to V belt drive. They originaly ran with a two speed 3 phase motor he had put a single speed 1425 rpm into it. The machine was designed to run at a maximum of 2000 rpm but can't get halve that with his pulley arrangement ie 2 inch on the motor to 6 on the countershaft then 4-3 and 2 from countershaft to the same on the head.

Any suggestions for changing motor to countershaft pulleys to give a reasonable speed range, I only use cutters from 1/8 to 1/2 inch plus occasional fly cutter on usual metals ie brass and steel so also need to get the revs down a bit as well. Thanks David

[david newman 9Participant @davidnewman9]

[JasonBModerator @jasonb]

I would have thought you could get down to a lot less than half with those pullies

2" to 6" is 1:3 reduction so you have 475rpm at the counter shaft.

2" on the countershaft to 4" on the spindle is 1:2 reduction so that would give 237.5rpm at the spindle.

3" on both is 475rpm

4" counter to 2" spindle gives 950rpm.

J

[Clive FosterParticipant @clivefoster55965]

How difficult is it to change the belt on the motor to countershaft pulley drive? If things are reasonably accessible a quick and dirty expedient is to mount two sizes of pulley on both motor and countershaft chosen so the pairs give you appropriate high and low speed ranges. Get a two belts, one for each pulley pair, of lengths calculated to give very close centre distances. Generally a variation of less than 1/4" or so can be arranged. A reasonably hefty spring in the belt tensioning arrangement will accommodate that or you could go all posh with a spring loaded jockey pulley. If you decide to go for a jockey pulley it would be worth investigating whether light modification of a car fan or camshaft drive belt tensioner assembly could suffice saving on building work.

Although it sounds bodgey the two belt system worked well enough for me in one application for several people to copy it. Second time round I did it properly and worked out a set of pulleys to do the job with a single size of belt. Even with computer assistance the gain was not, objectively, worth the headache.

Clive

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